where t is the texture that is directly feed into the method from the FrameBuffer's blit-method. However, some dispose or remove-methods clear that reference when executed in another thread, especially when finalizing the framebuffer. Might be that the old framebuffer get's finalized and that triggers the clear process...i'll see what to do to fix this...

Yes, i'm sure...but i wasn't aware that i'm calling this method... The problem seems to be, that the blitting happens in parallel with your freeMemory()-call. I can't really handle this 100%. I've uploaded a new jar that tries to, but there's still room for failure. Can you synchronize the freeMemory call somehow?

It's a bit complicated. AE uses some static Object arrays to store data, like the the data that is passed down to the renderer for blitting. These buffers need some cleanup from time to time or otherwise. they'll keep references to unused objects for ever. freeMemory() removes references to the frame buffer from these buffers but if the renderer tries to blit that thing on this moment, it get null instead of the (now invalid) buffer.